#include<bits/stdc++.h>
using namespace std;
int main(){
	int i=0,n,m=0;
	cin>>n;
	for(i=0;m<=n;i++){
		i=i+m;
		m+1;
	}
	cout<<i;
}
/**************************************************************
	Problem: 1002
	User: huxuanchen
	Language: C++
	Result: Time Limit Exceed
****************************************************************/